Manufacture of carbon fibres

ABSTRACT

The invention relates to an improvement in a process for the production of carbon fibre (also filaments and films) from organic material consisting mainly of hydrocarbons (e.g. pitch, tars, solutions or extracts of coal). The organic material is spun or extruded to form a fibre, oxidised to stabilise it to heat treatment and subsequently carbonised. The invention comprises employing as an additive in the organic material from 0.05 percent to 30 percent by weight of one or more polymers compatible with the organic material and thoroughly mixed therewith, provided that if the polymer is aromatic, it has a molecular weight of above 5000. Typical polymers include vinyl chloride polymers, vinyl acetate polymers, polymethacrylates, and polypropylenes.

United States Patent [191 Powell et al.

[ 1 Dec.3, 1974 1 MANUFACTURE OF CARBON FIBRES [73] Assignee: Coal Industry (Patents) Limited,

London, England 22 Filed: Aug. 24, 1971 21 Appl. No.: 174,552

[30] Foreign Application Priority Data Sept. 8, 1970 Great Britain 42992/70 [52] US. Cl. 423/447, 264/29, 264/176 F [51] Int. Cl C0lb 31/07 [58] Field of Search 23/2091, 209.1 F, 209.4;

[561 References Cited UNITED STATES PATENTS 1,925,005 3/1933 Rose 44/1 3,392,216 7/1968 Otani r 1 264/29 3,395,970 8/1968 Machell 1 23/2091 X 3,529,934 9/1970 Shindo 23/2091 3,576,907 4/1971 Kimura ct 264/176 F 3,607,672 9/1971 Schmitt 1 1 23/2091 3,629,379 12/1971 Otani 23/2091 3,639,953 2/1972 Kimura et a]. 23/209 1 3,723,609 3/1973 Mansmann ct a1. .1 423/447 3,784,679 1/1974 Chichc 423/447 OTHER PUBLICATIONS MacKay, et 211., Modern Plastics, Vol. 45, No. 2, 1968, pages 147-150.

Primary ExaminerEdward J. Meros Attorney, Agent, or Firm-Stevens, Davis, Miller & Mosher [57] ABSTRACT The invention relates to an improvement in a process for the production of carbon fibre (also filaments and films) from organic material consisting mainly of hydrocarbons (e.g. pitch, tars, solutions or extracts of coal). The organic material is spun or extruded to form a fibre, oxidised to stabilise it to heat treatment and subsequently carbonised. The invention comprises employing as an additive in the organic material from 0.05 percent to 30 percent by weight of one or more polymers compatible with the organic material and thoroughly mixed therewith, provided that if the polymer is aromatic, it has a molecular weight of above 5000. Typical polymers include vinyl chloride polymers, vinyl acetate polymers, polymethacrylates, and polypropylenes.

4 Claims, No Drawings MANUFACTURE OF CARBON FIBRES nising the stabilised fibre, filament or film, whereby a fibre, filament or film consisting essentially of carbon is formed.

British Pat. No. l 071 400 describes such a process wherein the organic material consisting mainly of hydrocarbons comprises a substance exhibiting a molten state resulting from baking in an oxygen-free atmosphere at a temperature of from 300 to 500C an organic substance selected from the group consisting of natural or synthetic organic substances which will produce said molten substance as a result of said baking. Examples of the natural or synthetic organic substances alleged to be suitable for use in the process of British Pat. No. l 071 400 include synthetic high polymeric substances such as polyvinyl chloride and polyacrylonitrile, natural organic substances such as petroleum pitch or asphalt, bitumen, coal and coal pitch, and pitches and tars formed by distillation or pyrolysis in the manufacture of certain organic compounds.

British Pat. No. l 091 890 describes a similar process to that of British Pat. No. l 071 400 wherein the organic material consisting mainly of hydrocarbons com- .prises a pitch or pitch'like substance having a C/H atomic ratio between 0.85 and 1.60 and a mean molec ular weight of not less than 400. Such pitches or pitchlike substances may include petroleum pitches, coal-tar pitches and pitches produced as by-products in various industrial processes. Pitches having the requisite properties may be formed by transformation of other pitches for example by heating, optionally in the presence of additives such as inorganic halides e.g. aluminium trichloride or organic peroxides, e.g. dicumyl peroxide.

Copending application for United Kingdom Pat. No. 42675 dated August 27, 1969, corresponding to US. Pat. application No. 67,600, filed August 27, 1970, now abandoned, describes and claims a process for producing fibres, filament or films consisting essentially of carbon which comprises spinning or extruding a so lution or extract of coal to form a fibre, filament or film, oxidising the spun or extruded fibre, filament or film to form a fibre, filament or film stabilised to heat treatment and carbonising the stabilised fibre, filament or film.

By solution or extract of coal it is meant to include those products formed by the treatment of coals with high boiling aromatic solvents, but other solvents, for example chloroform and pyridine, may also be employed. By high boiling aromatic solvents it is meant to include those solvents boiling above'about 200C and which contain at least one aromatic ring. Such solvents are known, in general, to dissolve or extract at least a portion of the aromatic matter from coal. The dissolution or extraction may include degradation of the coal molecules, whether solvolytically or otherwise, and it is not intended to imply that no chemical reactions take place. Suitable solvents include polynuclear aromatic hydrocarbons, for example phenanthrene, although it will not be normal to employ pure compounds as solvents for economic reasons. Mixtures of high boiling hydrocarbons formed from coal are particularly suitable solvents, for example anthracene oils. Hydrogenated polycyclic hydrocarbons may be used but these normally react with the coal in a well-known manner and hydrogenate the coal, forming aromatic hydrocarbons, and can therefore not be recovered; for example, tetralin is dehydrogenated to naphthalene. It may sometimes be convenient to form the solution or extract of coal by so treating the coal in the presence of hydrogen gas which reacts with the coal. ln the case where a low boiling point solvent has been employed to produce a solution or extract of coal, it is preferred to employ substantially solvent-free extract of coal produced from such a solution or extract. The term solution or extract of coal is not intended to be limited to products formed by the liquid phase dissolution or extraction of coal but to include those products formed by treating coal, or a solution or extract thereof,-with a solvent in the gaseous phase, at either above or below the critical pressure and temperature of the gaseous solvent, and condensing the portion of the coal dissolved on entrained in the gaseous solvent. Such solvents are not limited to those that are liquid at ambient conditions but may include, for example, ethylene and other gases. Any coal may, in principle, be employed to form the solution or extract. The term coal is intended to include materials that are of a coal-like nature and which contain dissolvable material, for example lignite.

The solution or extract of coal is then spun or extruded at a temperature generally just above the melting or softening point of the solution or extract. The fibre, filament or film so spun or extruded may be drawn or stretched during or immediately after spinning or extrustion in order to form the fibre, filament or film to be heat treated. The spun or extruded fibre, filament or film is then oxidised, preferably under a small tension, to stabilise the fibre, filament or film to heat treatment, rendering it infusible. The oxidation may be carried out in an oxidising atmosphere, for example air, oxygen or ozone, at an elevated temperature, for example 250C. The stabilised fibre, filament or film is then heated, preferably under a small tension, to a temperature within the range of 600C to 3,000C in an inert atmosphere to carbonise it.

The present invention provides an improvement in a process for the production of fibres, filament and films consisting essentially of carbon by spinning or extruding organic material consisting mainly of hydrocarbons to form a fibre, filament or film consisting of the organic material, oxidising the fibre, filament or film whereby the spun or extruded fibre, filament or film is stabilised to heat treatment and carbonising the stabilised fibre, filament or film whereby a fibre, filament or film consisting essentially of carbon is formed, wherein the organic material consisting mainly of hydrocarbons contains from 0.05 to 30 percent, and desirably from 0.1 to 20 percent, by weight of additive comprising one or more polymers compatible with. the organic material and thoroughly mixed therewith, provided that the polymer, if aromatic, has a molecular weight of above 5,000. Preferably the polymer, if aliphatic, has a molecular weight of above 5,000.

The effect of the additive is, in general, to alter the viscosity characteristics of the organic material including the softening point, which may improve the spinnability of the organic material and increase the strength of the spun or extruded fibre, filament or film. This may give improved resistance to fracture of the fibre, filament or film and improve the handlability thereof. The effect of the additive may be to enable the spun or extruded fibre, filament or film to be stabilised to heat treatment more rapidly by allowing it to be heated at a higher rate. This is of considerable commercial importance since a major proportion of the cost of manufacture of the carbon fibre, filament or film is the processing, especially the heating, of the spun or extruded fibre, filament or film. The addition of the additive may also have an effect on the carbonisation of the stabilised fibre, filament ,or film.

The polymers that may be employed as additives are in no way limited to those that form carbon fibres themselves when suitably processed. Indeed, polymers that have large effects include those which are not suitable for conversion into carbon fibres, for example vinyl chloride polymers and analogous polymers and acrylate polymers.

Suitable polymers that may be employed as additives include polyethylenes, polypropylene, ethylene/vinyl acetate copolymers, ethylene/propylene rubber, natural and synthetic rubbers including rubbers derived from butadiene, styrene, acrylonitrile, and isoprene, including copolymers of such monomers, and halogenated rubbers, polyacrylonitrile, polyesters, polyurethanes, cellulose and derivatives thereof, including regenerated cellulose, alkylated and acylated cellulose, and polyvinyl acylates and polyvinyl alcohol and derivatives intermediate polyvinyl acylates and alcohols. The preferred polymers for use as additives are those having at least 50 percent, and preferably at least 75 percent, of monomers or comonomers selected from vinyl chloride, vinylidene dichloride, vinyl acylates, for example vinyl acetate, acrylates and methacrylates, including acrylic acid and methacrylic acid and esters thereof, for example methylmethacrylate, acrylonitriles, for example acrylonitrile, and styrene.

It will be understood from the foregoing that these additives are applicable in any process in which any organic material consisting mainly of hydrocarbons is so treated. in particular, the organic material consisting mainly of hydrocarbons may be one of those described in British Pat. No. l 071 400 or 1 091 890 hereinbefore referred to. The organic material consisting mainly of hydrocarbons may be an extract or solution of coal described in application for United Kingdom Pat. No. 42 675 dated August 27, 1969. It will be understood that such solutions or extracts of coal, as well as pitches, pitch-like material and tar, derived from coal, will contain compounds other than hydrocarbons, particularly heterocyclic aromatic compounds for example pyridines, pyrroles and fused-ring derivatives thereof, and phenols, generally in amounts which are under percent of the total weight of the organic material. For the avoidance of doubt, it is to be understood that materials of such kind containing quantities of nonhydrocarbon matter as is found in material of such types as are hereinbefore described are to be considered as organic materials consisting mainly of hydrocarbons for the purposes of the present invention.

Other modifications to the organic material consisting mainly of hydrocarbons may be applicable in connection with the present invention. Other additives may be mixed with the organic material consisting mainly of hydrocarbons. The organic material consisting mainly of hydrocarbons may have been formed by subjecting a material falling within this class to a chemical treatment. Examples of these are given in Applications for United Kingdom Pat. Nos. 42 991 and 42 995, both dated Sept. 8, 1970.

It will be understood that various organic materials which have been subjected to various oxidation treatments to stabilise the spun or extruded fibres, filaments or films to heat treatment have various maximum rates of heating depending on their nature and history.

The invention will now be illustrated by nonlimitative examples of processes according to the invention.

EXAMPLE 1 A coal extract was produced by treating a bright coal of 84 percent carbon content, calculated on a dry, mineral-m'atter free, basis, with three times its weight of anthracene oil at 400C under pressure in an inert atmosphere. The coal extract was filtered and excess anthracene oil was distilled off at about 300C and 10 torr to leave a coal extract containing about equal quantities of material derived from the coal extracted and anthracene oil. 5 percent by weight, based on the weight of the coal extract, of a polypropylene was added to the extract and thoroughly mixed at 250C under nitrogen until the polypropylene was completely dissolved or dispersed (about 5 mins.)

The coal extract so prepared with the polypropylene dissolved or dispersed therein was extruded through a 380 ,am die at a temperature of 230C and drawn at a draw rate of m/min. to produce a continuous ex truded fibre. A tow of about 500 fibres so extruded, about 100 to 200 mm long was suspended in an oven and kept straight under a tension of about 1 mg/fibre during subsequent processing. The tow of fibres was heated in oxygen to 240C at a rate of 43C/min. and then in nitrogen at a rate of 50C/h to 1,000C at which temperature the tow was treated for 1 hour.

The fibres had diameters of about 11.4 am, tensile strengths of about 0.87 GN/m and Youngs moduli of about 44 GN/m (mean values in each case).

EXAMPLE 2 Example 1 was repeated except that a methyl methacrylate polymer was substituted for the polypropylene. The heating in oxygen was at 20C/min. to 300C.

The fibres had diameters of about 12.5 am, tensile strengths of about 0.87 GN/m and Youngs moduli of about 49 GN/m It was noted empirically in both cases that the extruded fibres broke less and were easier to handle than similar fibres without the polymeric additives. The fibres made without employing the polymeric additives could not be heated more rapidly than 2.6C/min. during the oxidation.

We claim:

1. In a process for the production of fibers, filaments or films consisting essentially of carbon by spinning or extruding organic material consisting mainly of hydrocarbons selected from the group consisting of an extract of coal, pitch from coal, tar from coal and a bitumen to form a fiber, filament or film of said organic maene and polymethylmethacrylate.

2. The process of claim 1, wherein the polymer has at least 50 percent of its monomers of methylmethacrylate.

3. The process of claim 1, wherein the polymer has at least percent of its monomers of methylmethacrylate.

4. The process of claim 1, wherein the polymer has as the monomer or monomers thereof propylene. 

1.IN A PROCESS FOR THE PRODUCTION OF FIBERS, FILAMENTS OR FILMS CONSISTING ESSENTIALLY OF CARBON BY SPINNING OR EXTRUDING ORGANIC MATERIAL CONSISTING MAINLY OF HYDROCARBONS SELECTED FROM THE GROUP CONSISTING OF AN EXTRACT OF COAL, PITCH FROM COAL, TAR FROM COAL AND A BITUMEN TO FORM A FIBER FILAMENT OR FILM OF SAID ORGANIC MATERIAL; OXIDIZING THE FIBER, FILAMENT OR FILM WHEREBY THE SPUN OR EXTRUDED FIBER, FILAMENT OR FILM IS STABILIZED TO HEAT TREATMENT AND CARBONIZING THE STABILIZED FIBER, FILAMENT OR FILM WHEREEBY A FIBER, FILAMENT OR FILM CONSISTING ESSENTIALLY OF CARBON IS FORMED; THE IMPROVEMENT WHEREBY THE SAID ORGANIC MATERIAL SPUN OR EXTRUDED CONSISTING OF HYDROCARBONS CONTAINS AS AN ADDITIVE THOROUGHLY DISSOLVED OR DISPERSED IN SAID ORGANIC MATERIAL FROM 0.05 TO 30 PERCENT BY WEIGHT OF ONE OR MORE POLYMERS COMPATIBLE WITH SAID ORGANIC MATERIAL AND BEING SELECTED FROM THE GROUP CONSISTING OF POLYPROPYLENE AND POLYMETHYLMETHACRYLATE.
 2. The process of claim 1, wherein the polymer has at least 50 percent of its monomers of methylmethacrylate.
 3. The process of claim 1, wherein the polymer has at least 75 percent of its monomers of methylmethacrylate.
 4. The process of claim 1, wherein the polymer has as the monomer or monomers thereof propylene. 